a) Field of the Invention
The present invention relates to an unequal-torque coil spring and a spring motor thereof, and more particularly to an unequal-torque coil spring that is applied to a curtain set which can automatically fold a curtain and used to provide a feedback torque thereto, thereby achieving objective of providing a feedback force corresponding to an actual requirement from different stages of a curtain-folding working process.
b) Description of the Prior Art
For the purpose of safely using curtains, designs of curtain sets without exposed pull cords have been tirelessly developed in the industry. As shown in FIG. 1, a curtain set 1 uses a spring motor 2 to produce a feedback force; after a lower beam 14 is pulled downwards and becomes lowered, a downward pulling force from a pull cord 12 is transmitted and stored in an equal-torque coil spring 20 inside of a spring motor 2 via a first reel drum 21 and a second reel drum 22. When a curtain 15 is folded back, the force stored in the spring motor 2 can be fed back and output to the lower beam 14, so that a safe design in which the curtain 15 can be folded back by a self-generated force without a pull cord may be applied.
Further, the spring motor 2 employs an elastic reaction force of approximately equal torque from a strip of equal-torque coil spring 20 to drive the first reel drum 21 and the second reel drum 22 at two sides, so as to reversely reel back the pull cord 12 at both sides and pull up the lower beam 14 by using the force stored in the equal-torque coil spring 20, thereby achieving the objective of folding back the curtain 15. To lower the curtain 15, a user pulls the lower beam 14 downwards, and an action force is transmitted to the first reel drum 21 and the second reel drum 22 via the linkage of the pull cord 12 and the turning of a turning component 13, and then the force is reversely output to the equal-torque coil spring 20 for storage via the first reel drum 21 and the second reel drum 22, so that the force can be used to fold back the curtain 15 later.
The equal-torque coil spring 20 is of a spiral shape, and generates an effective torque curve that is close to being horizontal, which is difficult to match the gravity force of unequal masses accumulated from setting the curtain 15 to different heights. Therefore, it is often necessary to add weights that are hung from the curtain and repeatedly adjust a torque value of a single curtain set 1 during production, in order to achieve a steady folding speed.
Referring to FIGS. 2 and 3, the spring motor 2 comprises a housing 201 assembled and provided with an axle 23 being combined with a chainring 230, and a coiling axle 24 being combined with a linking chainring 240; the chainring 230 and the linking chainring 240 are engaged with each other, and have the first reel drum 21 and the second reel drum 22 pivoted and disposed longitudinally at a front end and a rear end, respectively; the first reel drum 21 and the second reel drum 22 are respectively provided with a first chainring 210 and a second chainring 220, which are respectively engaged with the chainring 230 and the linking chainring 240. A detachable bearing 231 is sleeved outside of a cylindrical surface of the axle 23, and a cylindrical surface of the detachable bearing 231 allows a spiral inner circle of the equal-torque coil spring 20 to sleeve on; a release end of the equal-torque coil spring 20 is a joining end 200 which is joined to a radial cylindrical surface of the coiling axle 24.
Referring back to FIG. 1, when the lower beam 14 is pulled downwards, the generated force is released from the axle 23 to the coiling axle 24 as the equal-torque coil spring 20 is coiled around by the coiling axle 24, and the affected equal-torque coil spring 20 will generate a recovery coiling force (feedback force), when the lower beam 14 is pushed upwards, the feedback force from the equal-torque coil spring 20 is activated and released to reverse the equal-torque coil spring 20 back to the position of the axle 23. The reverse process happens as follows: the linking chainring 240 of the coiling axle 24 drives the second reel drum 22 via the second chainring 220 and then drives the first reel drum 21 via the chainring 230, so that the pull cord 12 at both sides are reeled back by linking the first reel drum 21 and the second reel drum 22.
In the aforesaid process, a coiling speed of the equal-torque coil spring 20 is different from that of the chainring 230 due to the presence of the detachable bearing 231, the chainring 230 solely serves the purpose of shifting the force in this case, and shifts a force resulted from the first reel drum 21 being pulled by the pull cord 12 and transfers the force to the linking chainring 240 of the coiling axle 24. Similarly, when the second reel drum 22 at the right is pulled by the pull cord 12, the second chainring 220 can also transfer the force to the coiling axle 24, so that the coiling axle 24 can pull and coil the equal-torque coil spring 20, and the equal-torque coil spring 20 sequentially releases the force and turns around a center of a diameter thereof when it is pulled and coiled around by the coiling axle 24.
Referring to FIG. 4, which shows the curtain 15 that has been folded upwards completely. When the disposed lower beam 14 is pulled by the pull cord 12 and moved upwards, each curtain piece 150 is sequentially accumulated on an upper surface of the lower beam 14; consequently, a plurality of curtain pieces 150 are accumulated and form a total mass W of the stacked curtain pieces, which results in a maximum pulling force from the pull cord 12 at this moment. In comparison, the pull cord 12 also withstands the maximum pulling force at this moment, and holds the lower beam 14 to keep it from falling downwards.
When the curtain piece 15 is completely lowered, the lower beam 14 is at a lowest position which is a fifth height H5, and the pulling force withstood by the pull cord 12 is the minimum at this moment as it only needs to support the mass of the lower beam 14 now. Therefore, within the range of a total lift height H0, as the lower beam 14 has the curtain pieces 150 accumulated on top of it one by one from the bottom, the weight load of the curtain pieces 150 gradually increases as a result, and the weight load reaches maximum when the lower beam 14 reaches the top, and becomes minimum when the lower beam 14 is at the bottom.
In addition, when it reaches a third height H3 defined in the curtain folding process, the spring motor 2 needs to produce a balancing pulling force against the lower beam 14 when it is located at the third height H3, so as to prevent the lower beam 14 from falling downwards, while the spring motor 2 also needs to avoid producing excessive pulling force that pulls the lower beam 14 upwards.
When the lower beam 14 is located at the lowest position which is the fifth height H5, and being pulled upwards to a first height H1, an upward momentum is generated from the combined factor between a mass of the lower beam 14 and a pulling speed of the pull cord 12. Therefore, it would be ideal to have the pulling force from the pull cord 12 lessened when the lower beam 14 reaches a second height H2, so as to achieve a buffering effect, and then have the spring motor 2 output a smaller torque again in order to slowly pull up the lower beam 14 located at the second height H2 to the first height H1, so as to prevent the momentum from the lower beam 14 to impact on a lower part of an upper beam 11.
Referring to FIG. 5, two sides of each of the curtain pieces 150 are respectively combined with ladder strings 120 at two sides, and two ladder strings 120 form a top-to-bottom linkage between a pitch P to support the curtain pieces 150. Consequently, each of the curtain pieces 150 are linked from top to bottom, and topmost ends of the ladder strings 120 are combined with the upper beam 11. As shown in the figure, when the lower beam 14 is located at a half-height position Hn, the weight of the total mass W of the stacked curtain pieces is withstood by the upper surface of the lower beam 14; when the pull cord 12 is pulling upwards or supporting the curtain in a fixed position, the ladder strings 120 help support the total weight of all curtain pieces 150 interspaced by the pitch P.
As the lower beam 14 is lowered, the feedback torque stored in the spring motor 2 is needed for fixing the lower beam 14 at the half-height Hn position, while the upper surface of the lower beam 14 is supporting the total mass W of the stacked curtain pieces at Hn at the same time. Thus as the lower beam 14 moves upwards, greater balancing torque is needed from the spring motor 2. In contrast, as the lower beam 14 moves downwards, the torque needed from the spring motor 2 declines proportionately. Subsequently, the required working torque curve from the spring motor 2 turns from steep to flat.
To allow the spring motor 2 of the curtain set 1 to produce the torque needed for folding back the curtain 15 during the curtain folding process, as disclosed in U.S. Pat. No. 6,283,192 B1; the main technical feature is related to the longitudinal area of a strip of spring, and a method of boring holes to form weak points is utilized to distribute bore holes of unequal sizes and distances, so that the strip of spring can have different elastic actions at a front end and a back end. For producing feedback torque output for actual system requirements based on simulations, and another U.S. Pat. No. 5,482,100, a strip of spring is formed with different thicknesses or widths at a front end and a back end in order to produce elastic reactions that result in varied torque to meet the actual requirements for torque. But the method of boring holes leads to weaknesses in the strip of spring, which results in the problems of mechanical damage and difficulty in processing. Further, because the strip of spring is a very thin metal slice that needs to have different thicknesses and widths at a front end and a rear end, the processing control for making increasing or decreasing thicknesses and widths needs to be extremely precise, which makes the production of the spring difficult and time-consuming.